The present invention relates to a permanent magnet embedment rotating electric machine, a motor for car air conditioner, and an enclosed electric compressor. The rotating electric machine includes a stator having coils and a rotor rotatably arranged in the stator. Permanent magnets are embedded as magnetic poles inside the rotor.
Permanent magnets are embedded inside the rotor of this type of rotating electric machine so as to be adjacent to each other in the circumferential direction of the rotor. A pair of the permanent magnets adjacent to each other in the circumferential direction of the rotor are arranged so as to have different polarities. Sudden magnetic flux density fluctuation occurs at a location between the two adjacent permanent magnets, that is, a magnetic pole switching part. Thus, torque pulsation occurs, which causes vibration and noise in the rotating electric machine. Hereinafter, the torque pulsation is referred to as torque ripple. The torque ripple represents fluctuation range of output torque of the rotating electric machine.
Japanese Laid-Open Patent Publication No. 2001-69701 discloses a motor that suppresses torque pulsation. The radius of a rotor is minimal at magnetic pole switching parts, and is maximum at central portions of permanent magnets, that is, magnetic pole centers. The rotor has an outer circumference having a sinusoidal waveform.
Japanese Laid-Open Patent Publication No. 2002-95194 discloses a motor having a rotor, parts of the outer circumference of which correspond to magnetic pole centers project outward into the shape of an arc.
Japanese Laid-Open Patent Publication No. 2002-136011 discloses a motor having a rotor, parts of the outer circumference of which correspond to magnetic pole centers form circumferential portions coaxial with the rotational center of the rotor. Parts of the outer circumference of the rotor in the vicinity of the ends of the adjacent magnetic poles of two permanent magnets are grooved.
In Japanese Laid-Open Patent Publication No. 10-285851, an iron core of the rotor has magnet insertion holes, which accommodate permanent magnets. The iron core has slits formed at portions outward of the magnet insertion holes.
However, in the motors of the above publications No. 2001-69701 and No. 2002-95194, the gap between teeth of a stator and the outer circumference of the rotor becomes minimal only at points. These points are portions corresponding to the magnetic pole centers in the side cross-section of the outer circumference of the rotor. Thus, a torque constant of the motor, that is, possible output torque per unit current is small compared to a case, for example, where the radius of the outer circumference of the rotor is constant through the entire circumference.
In the motor of the above publication No. 2002-136011, the gap between the teeth of the stator and the outer circumference of the rotor varies greatly between the circumferential portion and the grooved portions. Therefore, the torque pulsation is not easily suppressed. When the grooves are deep, the torque constant of the motor disclosed in the above publication No. 2002-136011 is smaller than the torque constant of the motor disclosed in the publications No. 2001-69701 and No. 2002-95194.
The publication No. 10-285851 describes that the slits prevent magnetic saturation of the teeth that face parts of the iron core toward the rotation direction of the rotor. However, the publication No. 10-285851 does not describe the relationship between the existence of the slits and suppression of the torque ripple.